Growers are being asked to send in brown rust samples from their fields, as researchers investigate why the disease ran riot in many crops this season.

The UK Cereal Pathogen Virulence Survey (UKCPVS) monitors pathogen populations and how virulence has changed.

This year researchers are investigating brown rust in wheat, after it started appearing in crops in March, three months earlier than usual.

Catherine Harries, senior crop protection scientist at the AHDB, says that because brown rust came into wheat crops at the young plant stage (before growth stage 55), all varieties except candidate Goldfinch were susceptible to it.

See also: Late-drilled oilseed rape escapes high flea beetle pressure 

This led to high brown rust pressure, which caused leaves to turn yellow through stress (see picture), rather than the brown pustules which are usually associated with the disease.

Catherine says there is evidence that the resistance provided by gene Lr24 may have been broken down by brown rust.

The variety Theodore contains that gene and is used as a septoria control on Recommended List (RL) sites, as it has a score of 9 for the disease, where 1 is the lowest and 9 the highest disease resistance.

Previously, Theodore had good brown rust resistance, but now has shown higher levels of the disease than Crusoe, which has a rating of 3 on the RL.

However, the UKCPVS needs farmers from all over the country to send in brown rust samples from any variety, to confirm whether resistance provided by Lr24 has broken down.

Mark Bollebakker, RL senior field trials manager at the AHDB, says one benefit of the high levels of brown rust seen in crops this season is the creation of more robust RL data for the disease.

He also questions whether the disease may at some point need reclassifying from its current medium importance level, if earlier infections become the norm due to milder winters.

Mark adds that in future, growers may need to take more account of brown rust resistance when choosing a variety.

Growers can find out how to send brown rust samples to the UKCPVS at the dedicated web page.

The UKCPV also welcomes wheat yellow rust samples and powdery mildew samples from barley.